Create an email with multiple attachment with resumable upload with Google Gmail Api

GmailResumableUpload.js

var fs = require('fs');
var request = require('request');
var EventEmitter = require('events').EventEmitter;
var mime = require('mime');
var util = require('util');

function gmailResumableUpload() {
	this.byteCount = 0; //init variables
	this.tokens = {};
	this.filepath = '';
	this.metadata = {};
	this.query = '';
	this.userId = '';
	this.retry = -1;
	this.host = 'www.googleapis.com';
	this.api = '/upload/gmail/v1/users/';
	this.api2 = '/drafts';
};

util.inherits(gmailResumableUpload, EventEmitter);

//Init the upload by POSTing google for an upload URL (saved to self.location)
gmailResumableUpload.prototype.upload = function () {
	var self = this;
	var options = {
		url: 'https://' + self.host + self.api + self.userId + self.api2 + '?uploadType=resumable' + self.query,
		headers: {
			'Host': self.host,
			'Authorization': 'Bearer ' + self.tokens.access_token,
			'Content-Length': 0,
			'X-Upload-Content-Length': fs.statSync(self.filepath).size,
			'X-Upload-Content-Type': 'message/rfc822'
		},
		body: JSON.stringify(self.metadata)
	};
	//Send request and start upload if success
	request.post(options, function (err, res, body) {
		if (err || !res.headers.location) {
			self.emit('error', new Error(err));
			self.emit('progress', 'Retrying ...');
			if ((self.retry > 0) || (self.retry <= -1)) {
				self.retry--;
				self.upload(); // retry
			} else {
				return;
			}
		}
		self.location = res.headers.location;
		self.send();
	});
}

//Pipes uploadPipe to self.location (Google's Location header)
gmailResumableUpload.prototype.send = function () {
	var self = this;
	var options = {
		url: self.location, //self.location becomes the Google-provided URL to PUT to
		headers: {
			'Authorization': 'Bearer ' + self.tokens.access_token,
			'Content-Length': fs.statSync(self.filepath).size - self.byteCount,
			'Content-Type': 'message/rfc822'
		}
	};
	try {
		//creates file stream, pipes it to self.location
		var uploadPipe = fs.createReadStream(self.filepath, {
			start: self.byteCount,
			end: fs.statSync(self.filepath).size
		});
	} catch (e) {
		self.emit('error', new Error(e));
		return;
	}
	var health = setInterval(function () {
		self.getProgress(function (err, res, body) {
			if (!err && typeof res.headers.range !== 'undefined') {
				self.emit('progress', res.headers.range.substring(8));
			}
		});
	}, 5000);
	uploadPipe.pipe(request.put(options, function (error, response, body) {
		clearInterval(health);
		if (!error) {
			self.emit('success', body);
			return;
		}
		self.emit('error', new Error(error));
		if ((self.retry > 0) || (self.retry <= -1)) {
			self.retry--;
			self.getProgress(function (err, res, b) {
				if (typeof res.headers.range !== 'undefined') {
					self.byteCount = res.headers.range.substring(8); //parse response
				} else {
					self.byteCount = 0;
				}
				self.send();
			});
		}
	}));
}

gmailResumableUpload.prototype.getProgress = function (handler) {
	var self = this;
	var options = {
		url: self.location,
		headers: {
			'Authorization': 'Bearer ' + self.tokens.access_token,
			'Content-Length': 0,
			'Content-Range': 'bytes */' + fs.statSync(self.filepath).size
		}
	};
	request.put(options, handler);
}

module.exports = gmailResumableUpload;

resumableUpload.js

var GmailResumableUpload = require('./GmailResumableUpload');

exports.createDraftWithClient = function (client, emailFileMailPath, cb) {

	var gmailResumableUpload = new GmailResumableUpload(); 

	gmailResumableUpload.tokens = client.credentials; //Google OAuth2 tokens
	gmailResumableUpload.userId = client.userId; // the gmail email
	gmailResumableUpload.filepath = emailFileMailPath; // file path of the email, since it's a large email containing attachment you should safe it as a file
	gmailResumableUpload.metadata = null;

	// some optional parameters
	gmailResumableUpload.query = '&supportsTeamDrives=true&';
	gmailResumableUpload.retry = 3;
	gmailResumableUpload.upload();

	gmailResumableUpload.on('success', function (success) {
		cb(null, JSON.parse(success))
	});

	gmailResumableUpload.on('error', function (error) {
		cb(error);
	});

};

Use Nodemailer to compose the email with the attachments, save the result to a file, then upload it with this.